I have also tried to listen very carefully to the questions and views expressed by Members on all sides of the House.

And I want to try and answer all the relevant questions today.

There are lots of different ways of putting them, but they boil down to this:

Why?

Why us?

Why now?

Is what we are contemplating legal?

Where are the ground troops to help us meet our objectives?

What is the strategy that brings together everything that we are doing, particularly in Syria?

Is there an end to this conflict and is there a plan for what follows?

So let me deal with each of these questions as directly as I can.

First, why?

Mr Speaker, the reason for acting is the very direct threat that ISIL poses to our country and to our way of life.

ISIL have attacked Ankara, Beirut and of course Paris…

…as well as the likely blowing up of a Russian plane with 224 people on board.

They have already taken the lives of British hostages…

…and inspired the worst terrorist attack against British people since 7/7 on the beaches of Tunisia.

And, crucially, they have repeatedly tried to attack us right here in Britain.

In the last 12 months, our police and security services have disrupted no fewer than 7 terrorist plots to attack the UK…

…every one of which was either linked to ISIL or inspired by their propaganda.

So I am in no doubt that it is in our national interest for action to be taken to stop them.

And stopping them means taking action in Syria – because it is Raqqa that is their HQ.

But why us?

Mr Speaker, my first responsibility as Prime Minister – and our first job in this House – is to keep the British people safe.

We have the assets to do that…

….and we can significantly extend the capabilities of the international coalition forces.

That is one reason why members of the international coalition…

…including President Obama and President Hollande…

…have made it clear to me that they want Britain to stand with them in joining air strikes in Syria as well as Iraq.

These are our closest allies – and they want our help.

Partly this is about our capabilities.

As we are showing in Iraq, the RAF can carry out what is called ‘dynamic targeting’…

…where our pilots can strike the most difficult targets at rapid pace and with extraordinary precision…

…and provide vital battle-winning close air support to local forces on the ground.

We have the Brimstone precision missile system, which enables us to strike accurately with minimal collateral damage – something that even the Americans do not have.

The RAPTOR pod on our Tornado aircraft has no rival…

…currently gathering 60% of the coalition’s entire tactical reconnaissance in Iraq, while also being equipped for strikes.

In addition, our REAPER drones are providing up to 30% of the intelligence in Syria but are not currently able to use their low collateral, high precision missile systems.

And we also have the proven ability to sustain our operations – not just for weeks, but if necessary for months into the future.

So Mr Speaker, of course we have these capabilities.

But the most important answer to the question, ‘why us’ is I believe even more fundamental.

And it’s this.

We shouldn’t be content with outsourcing our security to our allies.

If we believe that action can help protect us, then – with our allies – we should be part of that action…

…not standing aside from it.

And from this moral point comes a fundamental question.

If we won’t act now when our friend and ally France has been struck in this way…

…then our allies in the world can be forgiven for asking…

…if not now, when?

And that leads to the next question. Why now?

The first answer to that, of course, is because of the grave danger that ISIL poses to our security…

…a danger that has clearly intensified in recent weeks.

But there are additional reasons why action now is so important.

Just look at what has changed.

Not just the attack in Paris. But the world has come together and agreed a UN Security Council resolution.

And there is a real political process underway.

This could lead to a new government in Syria with whom we can work to defeat ISIL for good.

But as I explained to the House yesterday, we can’t wait for that to be complete before we begin acting to degrade ISIL and reducing their capability to attack us.

Let’s be clear about the military objectives that we are pursuing.

Yes, we want to defeat the terrorists, by dismantling their networks, stopping their funding, targeting their training camps and taking out those plotting terrorist attacks against the UK.

But there is a broader objective.

For as long as ISIL can pedal the myth of a so-called caliphate in Iraq and Syria…

…it will be a rallying call for Islamist extremists all around the world, and that makes us less safe.

Just as we have reduced the scale and size of the so-called caliphate in Iraq – increasingly pushing it out of Iraq – so we need to act in Syria.

Indeed, Mr Speaker, another reason for action now, is that the success in Iraq in squeezing the so-called caliphate is put at risk by our failure to act in Syria.

This border is not recognised by ISIL and we seriously hamper our efforts if we stop acting when we reach the Syrian border.

So when we come to the question ‘why now’, we have to ask ourselves whether the risks of inaction are greater than the risks of taking action.

Every day we fail to act is a day when ISIL can grow stronger and more plots can be undertaken.

Mr Speaker, that is why all the advice I have received – the military advice, the diplomatic advice and the security advice – all says yes, that the risks of inaction are greater.

Some have asked specifically whether taking action could make the UK more of a target for ISIL attacks.

So let me tell the House that the judgement of the Director General of the Security Service…

…and the Chairman of Joint Intelligence Committee…

…is that the UK is already in the top tier of countries that ISIL is targeting.

So I am clear that the only way to deal with that reality is to address the threat we face.

And to do so now.

Mr Speaker, let me turn to the question of legality.

It is a long-standing constitutional convention that we don’t publish our formal legal advice.

But the document I have published today shows in some detail the clear legal basis for military action against ISIL in Syria.

It is founded on the right of self-defence as recognised in Article 51 of the UN Charter.

The right of self‑defence may be exercised individually where it is necessary to the UK’s own defence…

…and of course collectively in the defence of our friends and allies.

Mr Speaker, the main basis of the global coalition’s actions against ISIL in Syria is the collective self-defence of Iraq.

Iraq has a legitimate government, one that we support and help.

There is a solid basis of evidence on which to conclude, firstly, that there is a direct link between the presence and activities of ISIL in Syria, and their ongoing attack in Iraq…

….and, secondly, that the Assad regime is unwilling and/or unable to take action necessary to prevent ISIL’s continuing attack on Iraq – or indeed attacks on us.

It is also clear that ISIL’s campaign against the UK and our allies has reached the level of an ‘armed attack’ such that force may lawfully be used in self-defence to prevent further atrocities being committed by ISIL.

And this is further underscored by the unanimous adoption of UN Security Council Resolution 2249.

We should be clear about what this resolution means and what it says.

The whole world came together – including all 5 members of the Security Council – to agree this resolution unanimously.

The resolution states that ISIL, and I quote: “constitutes a global and unprecedented threat to international peace and security.”

It calls for member states, and again I quote: to take “all necessary measures” to prevent and suppress terrorist acts committed specifically by ISIL…

…and crucially is says that we should, and again I quote: “eradicate the safe haven they have established over significant parts of Iraq and Syria.”

Turning to the question of which ground forces will assist us.

In Iraq the answer is clear. We have the Iraqi security forces and the Kurdish Peshmerga.

In Syria the situation is more complex.

But as the report I am publishing shows, we believe there are around 70,000 Syrian opposition fighters – principally the Free Syrian Army – who do not belong to extremist groups…

…and with whom we can co-ordinate attacks on ISIL.

In addition there are the Kurdish armed groups who have also shown themselves capable of taking territory, holding territory, and administering it…

…and crucially relieving the suffering that the civilian population had endured under ISIL control.

The Syrian Kurds have successfully defended Kurdish areas in Northern Syria and retaken territory around the city of Kobane.

Moderate armed Sunni Arabs have proved capable of defending territory north of Aleppo…

…and they stopped ISIL’s attempts to capture the main humanitarian border crossing with Turkey and sweeping into Idlib province.

In the south of Syria, the Southern Front of the Free Syrian Army has consolidated its control over significant areas and has worked to prevent terrorists from operating.

These people I’ve talked about, they are ground troops. They need our help. When they get it, they succeed. So in my view we should do more to help them from the air.

But those who ask questions about ground troops are absolutely right to do so.

The full answer can’t be achieved until there is a new Syrian government that represents all the Syrian people – not just Sunni, Shia and Alawite, but Christian, Druze and others.

And it is this new government who will be the natural partners for our forces in defeating ISIL for good.

Mr Speaker, we can’t defeat ISIL simply from the air or purely with military action alone.

It requires a full political settlement.

But the question is: can we wait for that settlement before we take action?

And again, my answer is no, we can’t.

On the question about whether this is part of an overall strategy – the answer is yes.

Our approach has 4 pillars.

First, our counter-extremism strategy means we have a comprehensive plan to prevent and foil plots at home and also to address the poisonous extremist ideology that is the root cause of the threat we face.

Second, our support for the diplomatic and political process.

And we should be clear about this process.

Many across this House rightly said how vital it is to have all the key regional players around the table – including Iran and Russia.

And we are now seeing Iran and Saudi Arabia sitting down around the same table with America and Russia, as well as of course France, Turkey and Britain…

…and all of us working towards the transition to a new government in Syria.

Now the third pillar is the military action I am describing to degrade ISIL and reduce the threat they pose.

It is working in Iraq. And I believe it can work in Syria.

Now the fourth pillar is immediate humanitarian support but even more crucially, longer-term stabilisation.

Of course this House has heard many times that Britain has so far given over £1.1 billion – by far the largest commitment of any European country – second only to the United States.

…and this is helping to reduce the need for Syrians to attempt the perilous journey to Europe…

…and the donor conference I am hosting in February together with Germany, Kuwait, Norway and the UN, I believe that will help further.

But the House is rightly also asking more questions about whether there will be a proper post conflict reconstruction effort to support a new Syrian government when it emerges.

Britain’s answer to that question is absolutely yes.

I can tell the House that Britain would be prepared to contribute at least another £1 billion for this task.

So all these elements – counter-terrorism, political and diplomatic, military and humanitarian – they need to happen together to achieve a long-term solution in Syria.

We know that peace is a process not an event.

And I am clear that it can’t be achieved through a military assault on ISIL alone.

It also requires the removal of Assad through a political transition.

But I am also clear about the sequencing that needs to take place.

Mr Speaker, this is an ISIL first strategy.

What of the end goal?

So Mr Speaker, the initial objective is to damage ISIL and reduce its capacity to do us harm.

And I believe that this can, in time, lead to its eradication.

No-one predicted ISIL’s rise and we should not accept that it’s somehow impossible to bring them to an end.

They are not what the people of Iraq and Syria want.

They don’t represent the true religion of Islam.

And they are losing ground in Iraq, following losses in Sinjar and Baji.

Now we are not naïve to the complexity of the task.

It will require patience and persistence.

And our work won’t be complete until we have reached our true end goal…

…which is having governments in both Iraq and Syria which can command the confidence of all their peoples.

And in Syria, ultimately that means a government without Assad.

As Ban Ki Moon has said: “A missile can kill a terrorist; but only good governance can kill terrorism.”

This applies so clearly to both Iraq and Syria.

Mr Speaker, as we discuss all these things, people also want to know that we have learnt the lessons of previous conflicts.

Whatever anyone thought of the Iraq war…

…terrible mistakes were made in the aftermath in dismantling the state and the institutions of that country.

And we must never make those mistakes again.

The political process in Syria will, in time, deliver new leadership and it is that transition we must support.

We are not in the business of dismantling the Syrian state, or its institutions.

In Libya, the state and its institutions had been hollowed out after 40 years of dictatorship.

When the dictatorship went, the institutions rapidly collapsed.

But the big difference between Libya and Syria is that in Syria this time, we have firm international commitment from all the backers of a future Syrian government around the table at the Vienna talks.

The commitment is clear: to preserve and develop the state in Syria and allow a new representative government to govern for all its people.

So Mr Speaker, I have attempted to answer the main questions – why, why now, why us, is it legal, what are the ground forces, is there a strategy, what is the end point and what is the plan for reconstruction.

But I know this is a highly complex situation and I know Members on all sides will have other questions which I look forward to trying to answer this morning.

One will be about the confused and confusing situation in Syria with regard to Russia’s intervention.

Mr Speaker, let me reassure the House that the American-led combined air operations centre has a memorandum of understanding with the Russians.

This enables daily contact and pragmatic military planning to ensure the safety of all coalition forces. And this would include our brave RAF pilots.

Another question will be about whether we are taking sides in a Sunni versus Shia conflict.

This simply is not the case.

Yes ISIL is a predominantly Sunni organisation – but it is killing Sunnis and Shia alike.

Our vision for the future of Syria – as with Iraq – is not a sectarian entity, but one governed in the interests of all its people.

So we wholeheartedly welcome the presence of states with both Sunni and Shia majorities at the Vienna talks and their support for international action both against ISIL and towards a diplomatic solution in Syria.

The House will also want to know what we are doing about the financing of ISIL.

The document sets this out – and it includes intercepting smugglers, sealing borders…

…and enforcing sanctions to stop people trading with ISIL.

But ultimately ISIL is able to generate income through its control of territory.

So while we are working with international partners to squeeze the finances wherever we can…

…it is the rolling back of ISIL’s territory which will ultimately cut off its finances.

Two of the most complex questions in an undoubtedly complex situation are these.

First, will acting against ISIL in Syria actually help to bring about transition.

I believe the answer is yes – not least because there can’t be genuine transition without maintaining the territorial integrity of Syria.

ISIL completely deny with their current action this integrity.

Crucially, destroying ISIL helps the moderate forces – and these moderate forces will be crucial to Syria’s future.

Second, does our view that Assad must go help in the fight against ISIL. Or as some claim, does this confuse the picture.

The expert advice I have could not be more clear: we will not beat ISIL if we waiver in our view that ultimately Assad must go.

We cannot win over majority Sunni opinion – which is vital for the long-term stability of Syria – if we were to suddenly change our position.

Mr Speaker, in the end it comes back to this one main question – should we take action?

All those who say that ultimately we need a diplomatic solution and a transition to a new government in Syria – they are right.

Working with a new representative government is the way to eradicate ISIL in Syria in the long-term.

But can we wait for that to happen before we take military action?

I say we can’t.

Mr Speaker, let me be clear.

There will not be a vote in this House unless there is a clear majority for action…

…because we will not hand a publicity coup to ISIL.

Mr Speaker, I am also clear that any motion we bring before this House will explicitly recognise that military action is not the whole answer.

Proud as I am of our incredible servicemen and women – I will not pretend or overstate the significance of our potential contribution.

I will not understate the complexity of this issue…

…nor the risks that are inevitably involved in any military action.

But Mr Speaker, we do face a fundamental threat to our security.

We can’t wait for a political transition, we have hit these terrorists in their heartlands right now.

And we must not shirk our responsibility for security – or hand it to others.

Mr Speaker, throughout our history, the United Kingdom has stood up to defend our values and our way of life.